Known suspension systems typically used in North America for multi-axle heavy haul trailer applications include air ride suspensions, leaf spring-based systems and walking beam systems.
FIGS. 1 and 2 show another type of prior art suspension system, commonly known as a pendulum type hydraulic suspension, and that is sometimes used in heavy haul applications. In a pendulum type hydraulic suspension, the axle 10 pivots about a lower arm 12 that is in turn pivoted in relation to an upper arm 14 about a pivot pin 16. The upper arm 14 depends from a turntable plate 18 that rotates about a centre axis allowing the suspension assembly and its captive axle to rotate in relation to the frame of the trailer. A hydraulic cylinder 20 extends from the turntable plate 18 to the lower arm 12, the cylinder being located between the pivot pin 16 and the axle 10. Such a prior art system is also exemplified in FIG. 4 of U.S. Pat. No. 6,942,232 to McGhie.
In multi-axle trailers, each axle is independently suspended by its own pendulum type suspension. Equalization between the axles of an axle group tends to rely on fluid exchanges between the cylinders of the independent suspensions of the axle group. As one of the axles goes over a bump, the cylinder is compressed and the fluid moves to one or more other cylinders to support the load on the other axles. Equalization in pendulum type hydraulic suspensions can be more effective than in walking beam or air ride suspensions.
A disadvantage of this arrangement is that the location of the cylinder, being attached between the pivot point (the pivot pin) and the axle, does not provide the maximum possible mechanical advantage. The lack of an ideal mechanical advantage is compensated by providing more powerful cylinders. On the other hand, the system offers the advantage of providing the maximum effect for a minimum amount of piston stroke, since the cylinder is relatively close to the pivot point.
Independent hydraulic suspensions are sometimes used in heavy haul applications but not frequently so. However, they do offer the flexibility that is often needed in designing heavy haul applications that require various spacing between axles and axle groups.
Some jurisdictions, such as in the United States, allow what is known as “dual lane loading” for heavy haul vehicles. Dual lane loading allows the load to be spread over two lanes of a road using axles that extend across up to two lanes. This effectively increases the total weight allowance. In the prior art, dual lane loading is sometimes achieved by using walking beam types of suspensions and hydraulically telescoping the axles outward or inward as needed. When necessary, for example to cross a narrow bridge, the axles are telescoped inward to a narrower configuration and are brought back out for continued travel.
The applicant understands that telescoping of pendulum type independent hydraulic suspensions to achieve dual lane loading has been considered by some. However, telescoping the various hydraulic suspensions along with their captive axles and coordinating their movement is difficult. The practical resolution to the problem has been to provide systems wherein the hydraulic suspensions are unbolted, spacers or connectors are added or removed and the suspensions are re-bolted into a narrower or a wider configuration as the case may be. Such an approach is also exemplified in US Patent Publication No. 2009/0273159 (Sutton). It will be appreciated that that approach is unwieldy and time consuming.
It is therefore an object of this invention to provide a heavy haul vehicle that uses pendulum type hydraulic suspensions that is better suited for use with a telescoping system for accommodating dual lane loading applications.
These and other objects of the invention will be better understood by reference to the detailed description of the preferred embodiment which follows. Note that not all of the objects are necessarily met by all embodiments of the invention described below or by the invention defined by each of the claims.